The long-term goal of the proposed research is to understand the neural mechanisms underlying the control of motor output under normal and pathological conditions. The central hypothesis is that brainstem cholinergic systems contribute to motor preparation in much the same way that they are thought to contribute to sensory attention: by modulating activity in motor structures such that the movements most in line with behavioral goals are more likely to be executed. We examine this hypothesis in a robust anatomical projection of an advantageous animal model system: The cholinergic input from the brainstem pedunculopontine tegmental nucleus (PPT) to the intermediate gray layer of the superior colliculus (SC) in the mouse. The project goals will be achieved by recording and manipulating (using pharmacology and optogenetics) neural activity in freely-moving wild-type and transgenic mice performing behavioral tasks that require preparing and generating orienting movements. Aim 1 will examine how cholinergic input modulates SC activity and SC-dependent behavioral output. Aim 2 will focus directly on the activity of cholinergic PPT neurons during behavior. If successful, our proposal will elucidate, in a genetically accessible mouse model, key neural substrates underlying motor control. In addition to testing the specific hypotheses proposed here, the model we develop will make possible future research into how other genetically-defined networks of neurons contribute to motor output. Ultimately, understanding normal motor output can contribute to improving therapies for movement disorders, such as Parkinson's disease.